Greater predictability in the oral dosing of cyclosporin A (CSA) may minimize the number and duration of subtherapeutic or toxic events in organ transplantation, thus improving allograft survival. We have recently established that the bioavailability of the standard formulation of CSA (Sandimmune) in stable renal transplant recipients under steady state conditions is largely determined by both enteric and hepatic P4503A4 activity. Recently, a newly developed microemulsion formulation of CSA (Neoral) has demonstrated improved and more predictable bioavailability compared to Sandimmune. As a result, the improved correlation between trough CSA levels and AUC may facilitate the management of transplant patients, particularly those with CSA absorption difficulties. The improved pharmacokinetics associated with Neoral may be largely due to the ability of the microemulsified CSA to bypass enteric metabolism.